India arrested three citizens and said it was expelling a Pakistani high commission staffer for “espionage activities” on Thursday after busting a ring that collected documents on defence deployment and border area maps.

Delhi police joint commissioner Ravindra Yadav said Akhtar was detained on Wednesday with sensitive documents in his possession. The official was released after he invoked diplomatic immunity, Yadav said. Akhtar had been working with the Pakistan high commission in India for the past three years.

The two Indian citizens arrested on Wednesday were identified as Maulana Ramzan and Subhash Jangir, both residents of Rajasthan. They have been booked under the Official Secrets Act.

Indian nationals arrested over charges of spying for Pakistan.

“The Pakistan high commission official was the kingpin. He used to recruit Indians for spying and send information to Pakistan… The (spying) module was active for one-and-a-half years. We were working (to bust) it for the past six months,” Yadav said. “We recovered documents on defence deployment and border area maps. They had lists of BSF men who were deployed, transferred or retired,” he added.

The third person, a visa agent named Sohaib Nagaur, who was allegedly working as a spy for Pakistan’s ISI, was detained by the Rajasthan Police on Thursday.

Tensions between India and Pakistan have soared since an attack last month on an Indian Army base in Kashmir’s Uri killed 19 soldiers.

The Delhi Police officer said Akhtar and the arrested men were apprehended at the Delhi zoo on October 25 when they were meeting to exchange the documents. “On being questioned, the Pakistan high commission official identified himself as Mehmood Rajput. He had an Aadhaar card and said he was a resident of Chandni Chowk. When pressed more, he revealed he worked for the high commission... He invoked diplomatic immunity,” the police officer said.

This is not the first time that employees of the Pakistan High Commission have come under the radar over alleged espionage in India. Last year, police claimed to have busted an ISI spy ring in the high commission and five persons were arrested.